GEOPRIV WG J. Winterbottom
Internet-Draft M. Thomson
Intended status: Standards Track Andrew
Expires: September 3, 2007 B. Stark
BellSouth
March 2, 2007
HTTP Enabled Location Delivery (HELD)draft-winterbottom-http-location-delivery-05.txt
Status of this Memo
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Copyright Notice
Copyright (C) The IETF Trust (2007).
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Internet-Draft HELD March 20071. Introduction
The location of a Device is information that is useful for a number
of applications. A Device might be able to determine this
information using its own resources, but more often than not, the
Device must rely on its access network to provide this information.
This document describes a protocol that can be used to acquire
Location Information (LI) from a service within an access network.
This specification identifies two methods for acquiring LI. Location
may be retrieved from a Location Generator (LG) by-value, that is,
the Device may acquire LI directly. Alternatively, the Device may
request that the LG provide a location URI so that LI can be
distributed by-reference. Both of these methods are compatible, and
both can be provided concurrently from the same LG so that
application needs can be addressed individually.
This specification defines an XML-based protocol that enables the
retrieval of LI from a LG. This protocol can be bound to any
session-layer protocol, particularly those capable of MIME transport;
an HTTP binding is included as a minimum requirement.
1.1. Exclusions
This document defines a protocol for configuration purposes; that is,
a protocol for requesting (and receiving) the information necessary
to use LI. This document does not define a Geopriv Using Protocol.
The LG is assumed to be present within the same administrative domain
as the Device (the access network), which limits the security threats
that this protocol is exposed to.
This document does not specify how LI is derived. Determination of
the physical location of a network termination point is dependent on
the type of access network and the capabilities of networking
equipment. The specific methods that could be used are innumerable,
therefore this is left to individual network and equipment
implementations.
Providing LI by-reference implies that a server is able to provide
the Device with a public, globally-routable URI. How this URI is
provided is not covered by this specification. This includes any
interactions between the LG and LS necessary to facilitate the
provision of a Location URI.
This document does not define how an LG is discovered or configured.
Service discovery techniques are described in
[I-D.thomson-geopriv-lis-discovery].
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Internet-Draft HELD March 20071.2. Device or Target
LI provided for the Device is often represented as the location of a
user. However, in this document LI is attributed to a Device and not
a person. Primarily, this is because location determination
technologies are generally designed to locate a Device and not a
person. In addition to this, unless the Device requires active user
authentication, there is no guarantee that any particular individual
is using the Device at that instant. Thus, if any claim of veracity
is to be made for LI, the distinction between Target and Device must
be made explicit.
This distinction should not lead to the impression that the location
of the Device does not impact the privacy constraints required by
this protocol. Revealing the location of the Device almost
invariably reveals some information about the location of the user of
the Device, therefore the same level of privacy protection demanded
by a user is required for the Device.
It is expected that, for most applications, this distinction will be
unnecessary: LI for the Device will be used as an adequate substitute
for the user's LI. This requires either some additional assurances
about the link between Device and Target, or an acceptance of the
aforementioned limitations.
This document assumes that the Device is responsible for the protocol
interactions described and that it does so with the authority of the
Target and Rule Maker (RM).
1.3. The Bigger Picture
This document describes an interface between a Device and a Location
Generator (LG). Detailing the interactions between these two
entities requires a wider understanding of other interested parties.
For the Device, the most important consideration is the Target. In
some cases, this is the same as the Device, but it is more likely to
be a human user. The foundation of this protocol is that the Target
is able to direct the dissemination of LI, that is, the Target
provides authorization policies and otherwise controls how LI is
granted to Location Recipients (LRs). This extends to when a
Location Server (LS) is employed to provide a Location URI; the LS
cannot provide LI to an LR without express permission from the
Target.
The LG exists as an access network service. An Access Provider (AP)
operates this service so that Devices (and Targets) can retrieve LI.
The LG exists because not all Devices are capable of determining LI,
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Internet-Draft HELD March 20072. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This specification provides an XML Schema
[W3C.REC-xmlschema-1-20041028]. The schema definition is normative.
2.1. GEOPRIV Terminology
This document uses the terms (and their acronym forms) Location
Information (LI), Location Object (LO), Device, Target, Access
Provider (AP), Location Server (LS), Location Generator (LG),
Location Recipient (LR), Rule Maker (RM), Rule Holder (RH) and Using
Protocol as defined in [RFC3693].
For convenience, abbreviated versions of RFC 3693 [RFC3693]
definitions are included:
Access Provider (AP): An organization that provides physical network
connectivity to its customers or users, e.g., through digital
subscriber lines, cable TV plants, Ethernet, leased lines or radio
frequencies. Examples of such organizations include
telecommunication carriers, municipal utilities, larger
enterprises with their own network infrastructure, and government
organizations such as the military.
Civic Location/Address: A location expressed in a form that is
defined by civic demarcations. Civic addresses can be specialized
for jurisdictional (general use) or postal (message delivery)
purposes, or they can apply to either.
Device: The technical device whereby the location is tracked as a
proxy for the location of a Target.
Geodetic Location: A location expressed in coordinate form.
Location Generator (LG): The entity that initially determines or
gathers the location of the Target.
Location Information (LI): The data that describes the location of a
Device. Note that the term LI does not include the representation
of this data.
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Location Object (LO): An object conveying Location Information (and
possibly privacy rules) to which Geopriv security mechanisms and
privacy rules are to be applied [from 3693]; this is a specific
by-value representation of Location Information (LI). In this
document, LO refers to PIDF-LO [RFC4119].
Location Server (LS): The LS is an element that receives
publications of Location Objects from Location Generators and may
receive subscriptions from Location Recipients. The LS applies
the rules (which it learns from the Rule Holder) to LOs it
receives from LGs, and then notifies LRs of resulting LOs as
necessary.
In some specifications the Location Server is referred to as a
Location Information Server or LIS. Note that in this context,
the Location Server is distinct from what is alternatively
referred to as a Registrar in other contexts.
Location Recipient (LR): The entity that receives Location
Information (LI).
Rule Holder (RH): The entity that provides the rules associated with
a particular target for the distribution of Location Information
(LI).
Rule Maker (RM): The authority that creates rules governing access
to location information for a target (typically, this it the
Target themselves).
Target: A person or other entity whose location is communicated by a
Location Object (LO).
Using Protocol: A protocol that carries a Location Object.
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Internet-Draft HELD March 20073. HELD Overview
The HELD protocol facilitates retrieval of LI either by-value, as a
PIDF-LO document, or by-reference, as a Location URI.
This section describes how HELD can be used within a larger framework
that moves LI from a source (the LG) to a destination (the LR).
3.1. Requesting Location Information Directly
Where a Device requires LI directly, it can request that the LG
create a PIDF-LO document. The Device is then able to use the
provided PIDF-LO document as it is required, using the appropriate
application protocol. Figure 2 illustrates how this usage of HELD
fits within the model presented in [RFC3693].
+-----------+ +----------+ +-----------+
| Location | Location | Device | Location | Location |
| Generator |----Object--->| (Target) |----Object--->| Recipient |
| | | (LS, RH) | | |
+-----------+ +----------+ +-----------+
Figure 2: Simple Location Request Model
In this model, the Device in this scenario acts as a Location Server
(LS) and Rule Holder (RH); it is responsible for making authorization
decisions about which Location Recipients are given LOs.
The LG needs to uniquely identify the Device within the access
network. The source address of the request message is sufficient in
most cases. Once the Device is identified, the LG uses network
domain-specific information to determine the location of the Device.
An LI request does not need to include any identification information
other than return addressing. In fact, the HTTP binding (Section 7)
includes the option for a GET request. Return routability also
addresses a number of security concerns, see Section 8.
The response from the LG is a PIDF-LO document [RFC4119], unless
there were errors in processing the request.
The interface between Device (acting as LS) and Location Recipient
(LR) is application-specific and outside the scope of this
specification.
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Internet-Draft HELD March 20073.1.1. Shaping the PIDF-LO
A Device can include additional information in an LI request that
controls how the LG populates the fields in a PIDF-LO document.
Related to privacy, a presentity URI and usage rules can be
specified. The Device can also include a location estimate, or
request a specific type of location information, including a request
for a signed PIDF-LO.
When requesting LI, the Device can include a presentity URI for the
Target and a ruleset reference. The LG incorporates this information
in the PIDF-LO document, or modifies the document accordingly.
LI contained within a PIDF-LO document can be either geodetic
(coordinates using latitude and longitude or some other coordinate
system) or civic (street or postal addresses). The Device can
request that the LG provide a specific type of LI, including whether
a jurisdictional or postal civic address is required.
If a Device is capable of providing its own location it can include
this in a request. The LG is then able to include this LI in the
returned PIDF-LO. The type of LI is inferred from the request when
LI is provided.
The PIDF-LO document generated by an LG MUST follow the rules in
[I-D.ietf-geopriv-pdif-lo-profile]. The LI sent in a request MUST
follow the subset of those rules relating to the construction of the
"location-info" element.
3.2. Requesting a Location URI
Requesting LI directly does not always address the requirements of an
application. A Location URI is a URI [RFC3986] of any scheme, which
a Location Recipient (LR) can use to retrieve LI. A Device can
request a Location URI instead of LI.
Figure 3 illustrates how this usage of HELD fits within the model
presented in [RFC3693]. The first aspect of the diagram shows how
the Device acts as an agent for the Target and retrieves a Location
URI, which it then provides to the Location Recipient. The second
aspect has the Device acting as an agent for the Rule Maker; the
Device forwards rules to the LG, which forwards them to the LS.
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+-----------+ Location +--------------+
| Location |------URI------>| Device |
| Generator | | (Target) |
| |<-----Rules-----| (Rule Maker) |
+-----------+ +--------------+
| |
LO & Rules Location URI
| |
V V
+----------+ +------------+
| Location | Location | Location |
| Server |------Object----->| Recipient |
| | | |
+----------+ +------------+
Figure 3: Location URI Usage Model
Note that the Location Server takes the role of a (Private) Rule
Holder when the rules are provided by-value. The rules may also be
provided to the LG and LS by-reference, in which case, a Public Rule
Holder is required; the Public Rule Holder is not shown in this
diagram.
The interface between Device (acting as LS) and Location Recipient
(LR) is application-specific and outside the scope of this
specification. Also, any interface between Device (acting as RM) and
a Public Rule Holder is not relevant to this specification.
The merits and drawbacks of using a Location URI approach are
discussed in [I-D.marshall-geopriv-lbyr-requirements].
3.2.1. Establishing a Location Server Context
A Location URI is allocated for a Device by the LS. If the LS is to
be able to service queries for location directed at the Location URI,
it must maintain certain information. When the LG receives a request
for a Location URI, it requests that the LS allocate a URI for a
particular Device. As a part of providing a Location URI, the LS
also creates a _context_, which contains the information that it
requires to properly service requests to the URI.
This document does not make any normative statements about the
interface between the LG and LS. Any assumptions that are made about
the nature of this interface are stated where necessary.
A context contains sufficient information for the LS to identify the
Device to the LG, so that LI can be generated as required, which
could be on a per-request basis. The context also includes
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instructions from the Device on how the PIDF-LO is to be generated,
as described in Section 3.1.1.
The context contains an authorization policy that describes to whom,
and how, LI is granted. This is a common-policy document
[I-D.ietf-geopriv-common-policy] that is provided by the Device in
the context creation request, either directly, or by reference.
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Internet-Draft HELD March 20074. Protocol Description
As discussed in Section 3, this protocol provides two basic
functions: LI request and Location URI request. Messages are defined
as XML documents.
The Location Request message is described in Section 4.2. A Location
Request from a Device results in a PIDF-LO document in case of
success, or an error message.
In requesting a Location URI, the Device requests that a context be
created on the LS. The parameters for the create context request are
described in Section 4.3.1. The response to a context creation
request includes Location URIs and a password that can be used to
update the information contained in the context. The details stored
by the LS can be updated at any time after creation using the update
context request, described in Section 4.3.2.
Table 1 shows the basic set of messages supported by this protocol
and their respective responses, successful or otherwise.
+------------+------------------+-------------------+---------------+
| Operation | Request Message | Successful | Error |
| | | Response | Response |
+------------+------------------+-------------------+---------------+
| Request | locationRequest | PIDF-LO document | error |
| Location | (Section 4.2) | [RFC4119] | (Section 4.5) |
| | | | |
| Create | createContext | contextResponse | error |
| Context | (Section 4.3.1) | | (Section 4.5) |
| | | | |
| Update | updateContext | contextResponse | error |
| Context | (Section 4.3.2) | | (Section 4.5) |
+------------+------------------+-------------------+---------------+
Table 1: HELD Operations
A MIME type "application/held+xml" is registered in Section 10.5 to
distinguish HELD messages from other XML document bodies. This
specification follows the recommendations and conventions described
in [RFC3023], including the naming convention of the type ('+xml'
suffix) and the usage of the 'charset' parameter.
Section 5 contains a more thorough description of the protocol
parameters, valid values, and how each should be handled. Section 6
contains a more specific definition of the structure of these
messages in the form of an XML Schema [W3C.REC-xmlschema-1-20041028].
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Internet-Draft HELD March 20074.1. Protocol Binding
The HELD protocol is an application-layer protocol that is defined
independently of any lower layers. This means that any protocol can
be used to transport this protocol providing that it can provide a
few basic features:
o The protocol must have acknowledged delivery.
o The protocol must be able to correlate a response with a request.
o The protocol must provide authentication, privacy and protection
against modification.
Candidate protocols that could be used to address these purposes
include: TCP [RFC0793], TLS [RFC2246], SASL [RFC2222], HTTP
[RFC2616], SIP [RFC3261], BEEP [RFC3080] and SOAP
[W3C.REC-soap12-part1-20030624] [W3C.REC-soap12-part2-20030624].
This document includes a binding that uses a combination of HTTP, TLS
and TCP in Section 7.
4.2. Location Request
A location request is sent from the Device to the LG when it requires
LI. This request can be very simple, including no parameters; in
fact, the HTTP binding includes a GET request that does not include a
message body.
A Device MAY make an assertion about its own location as part of a
location request. Devices that have some means of acquiring LI,
either from embedded technology like Global Positioning System (GPS)
receivers or from user input, can use this to convey that information
to the LG. The "assert" element can be used to convey this
information.
The type of LI that a Device requests is determined by the type of LI
that is included in the "assert" element. When asserted LI is not
provided, the Device MAY specify the type of location requested using
the "locationType" element.
LI provided by the Device is potentially more precise than that
provided by the LG, therefore the LG MAY use this information to
create a response. The LG SHOULD validate the LI provided for
accuracy and precision before using this information.
The Device MAY specify a "profile" element that instructs the LG on
how to construct the LO. Alternatively, if the Device has created a
profile in an LS context, the Device can provide a "context" element
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so that the LG can retrieve the profile from the LS.
The location request is made by sending a document formed of a
"locationRequest" element. The successful response to a location
request is a PIDF-LO document, unless the request fails, in which
case the LG SHOULD provide an error indication document.
4.3. Contexts
A context is established by the LS in order to provide a Location
URI. The context includes information necessary to identify the
Device and determine its location when an LR requests an LO using the
Location URI.
4.3.1. Creating Contexts
The Device uses the "createContext" message to request that the LG,
and the LS, assign a Location URI. This establishes a context at the
LS.
The LS MUST maintain the information provided in the create context
request. The create context request includes a time limit, which
sets the maximum time that this context can be maintained.
The response to a create context request contains information that
the Device can use to identify a context. A set of Location URIs are
included, each one MUST uniquely identify the context; that is, the
LS MUST be able to identify a context based on a single Location URI.
A Device can distribute a Location URI to an LR to allow it retrieve
LI from the LS.
A Location URI MUST NOT contain any information that could be used to
identify the Device or Target. It is RECOMMENDED that a Location URI
contain a public address for the LS and a random sequence of
characters that the LS can use to identify a particular context. The
presentity identifier included in a PIDF-LO document SHOULD NOT be
used for either part or the entirety of a Location URI.
The response to a create context request MUST include the time when
the LS will terminate the context. The LS MUST NOT respond to any
queries to the context beyond this time. A response to a context
creation also includes a password that the Device uses to identify
itself when updating the context at any time before the context
expiry time.
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Internet-Draft HELD March 20074.3.2. Updating Contexts
A Device can update any of the information it has provided for a
context at any time. The update context request includes the same
information as the create context request with the addition of
information that identifies an existing context.
A Device uses any one of the Location URIs provided to uniquely
identify a context when updating context information. The context
password MUST be provided when updating context information.
If a Device includes an authorization policy (or ruleset) in an
update context request, the LS MUST refresh any stored copy of the
authorization policy. This is especially important for authorization
policies that are provided by-reference; the LS MUST update the
authorization policy, even if the URI has not changed. Updated
authorization policies MUST be processed by the LG and LS before any
subsequent requests from LRs are accepted; the LG and LS MAY defer
processing of the authorization policy until after a response is sent
to the Device.
The update context request is constructed using the "updateContext"
element. A successful response is the "contextResponse" element,
which is the same as the response to a create context response.
The update context request can also indicate that data can be removed
by the context by specifying a _nil_ value for any of the parameters,
using the "xsi:nil" attribute. This applies to the profile
(Section 5.4) element.
The response to an update context request is identical in form to the
create context response, with updated information about the context.
The Location URIs MUST be the same as those in the response to the
initial create context request, but the password and expiry time MAY
be changed.
4.3.3. Terminating Contexts
The update context request can be used to instruct the LS to
terminate a context. The "lifetime" element in the request is set to
a zero duration. Once the context has been terminated, or it has
expired, Location URIs that reference that context can no longer be
used and the Device MUST NOT use the Location URIs or password
relating to that context.
The LS MAY terminate a context without notifying the Device. The LS
SHOULD terminate contexts if it, or the LG, detect that any
information relating to the Device changes in a way that invalidates
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the context.
When the Device requests that a context be terminated, the LG
responds with a "contextResponse" message that does not include any
context information; this message MUST include the HELD "201"
response code.
4.4. Combined Context and Location Requests
HELD supports an optimization that allows for the creation or update
of a context while simultaneously requesting location information.
The optional "location" attribute on the "createContext" or
"updateContext" request can be used to request that the LG include a
PIDF-LO in the "contextResponse". This PIDF-LO is formed according
to the profile details associated with the context.
4.5. Indicating Errors
In the event of an error, the LG SHOULD respond to the Device with an
error document. The error response applies to all request types and
SHOULD also be sent in response to any unrecognized request.
An error indication document consists of an "error" element. The
"error" element MUST include a "code" attribute that indicates the
type of error. A set of predefined error codes are included in
Section 5.8.
Error responses MAY also include a "message" attribute that can
include additional information. This information SHOULD be for
diagnostic purposes only, and MAY be in any language. The language
of the message SHOULD be indicated with an "xml:lang" attribute.
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Internet-Draft HELD March 20075.1. "responseTime" Parameter
The "responseTime" attribute indicates to the LG how long the Device
is prepared to wait for a response. This attribute MAY be added to
any request message, although it is primarily used with the location
request. The value of this attribute is indicative only, the LG is
under no obligation to strictly adhere to the time limit implied; any
enforcement of the time limit is left to the Device.
This attribute MAY be either a duration value as defined in XML
Schema [W3C.REC-xmlschema-2-20041028], or a decimal seconds value,
which may include a decimal point. It is RECOMMENDED that systems
support millisecond precision for this parameter.
The LG SHOULD provide the most accurate LI that can be determined
within the specified interval. This parameter could be used as input
when selecting the method of location determination, where multiple
such methods exist. If this parameter is absent, then the LG SHOULD
return the most precise LI it is capable of determining.
5.2. "assert" Parameter
The "assert" element allows a Device to provide LI to the LG as part
of a location request. Two types of content are allowed: a geodetic
structure made up of a Geography Markup Language (GML) geometry
object, "_Geometry" as defined by [OGC.GML-3.1.1]; and a civic
address structure, "civicAddress" as defined by
[I-D.ietf-geopriv-revised-civic-lo]. The contents of this element
SHOULD follow the rules in [I-D.ietf-geopriv-pdif-lo-profile].
When used in combination with the "context" element, this LI MAY be
used by the LS for requests to Location URIs for that context.
This element is mutually exclusive with the "locationType" parameter,
defined in Section 5.3. The type of LI requested is implied by the
types included in the assertion.
5.2.1. "method" Parameter
The "method" attribute SHOULD be attached to the "assert" element to
indicate the means by which the LI was derived. This attribute
follows the rules of the similarly named method element of the
PIDF-LO.
5.2.2. "timestamp" Parameter
The "timestamp" attribute SHOULD be attached to the "assert" element
to indicate when the LI was generated.
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Internet-Draft HELD March 20075.2.3. "expires" Parameter
The "expires" attribute MAY be attached to the "assert" element to
indicate when the included LI is no longer valid. The LG SHOULD set
the "retention-expires" element in the returned PIDF-LO to no later
than this time if it uses the LI. This attribute SHOULD NOT be
included unless this time is definite.
5.2.4. "exact" Parameter
When the "exact" attribute is set to "true", it indicates to the LG
that the contents of the "assert" parameter MUST be strictly
followed. The default value of "false" allows the LG the option of
ignoring these values.
This attribute indicates that the asserted LI MUST be included in the
PIDF-LO response. If the LG cannot do this for any reason, which is
usually because it determines that the LI was inaccurate or
insufficiently precise, the LG MUST indicate an error.
5.3. "locationType" Parameter
The "locationType" element is included in a location request. It
contains a list of LI types that are requested by the Device. The
following list describes the possible values:
any: The LG SHOULD attempt to provide LI in all forms available to
it. This value MUST be assumed as the default if no
"locationType" is specified. The LG SHOULD return location
information in a form that is suited for routing and responding to
an emergency call in its jurisdiction.
geodetic: The LG SHOULD return a geodetic location for the Target.
civic: The LG SHOULD return a civic address for the Target. Any
type of civic address may be returned. The LG SHOULD ignore this
value if a request for jurisdictional or postal civic address has
been made and can be satisfied.
jurisdictionalCivic: The LG SHOULD return a jurisdictional civic
address for the Target.
postalCivic: The LG SHOULD return a postal civic address for the
Target.
The "locationType" element is mutually exclusive with the "assert"
element, defined in Section 5.2.
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The LG SHOULD return the requested location type or types. The LG
MAY provide additional location types, or it MAY provide alternative
types if the request cannot be satisfied for a requested location
type. If the "exact" attribute is present and set to "true" in a
location request, then a successful LG response MUST provide the
requested location type only, with no additional location
information. The "exact" attribute has no effect when this element
is set to "any".
The "SHOULD"-strength requirement on this parameter is included to
allow for soft-failover. This enables a fixed client configuration
that prefers a specific location type without causing location
requests to fail when that location type is unavailable. Unless the
"exact" attribute is set, the LG MUST provide LI in any available
form if it is unable to comply with the request.
For example, a notebook computer could be configured to retrieve
civic addresses, which is usually available from typical home or work
situations. However, when using a wireless modem, the LG might be
unable to provide a civic address.
5.3.1. "exact" Parameter
When the "exact" attribute is set to "true", it indicates to the LG
that the contents of the "locationType" parameter MUST be strictly
followed. The default value of "false" allows the LG the option of
ignoring these values.
A value of "true" indicates that the LG MUST provide a PIDF-LO that
includes LI of the requested type or types. The LG MUST provide the
requested types only and these types SHOULD be specified in the same
order as they were requested. The LG SHOULD handle an exact request
that includes a "locationType" element set to "any" as if the "exact"
attribute were set to "false".
5.4. "profile" Parameter
The "profile" element contains a presentity identifier [RFC2778] and
GEOPRIV usage rules [RFC4119] information. All fields are optional
within this element, but when these fields are included, the LG MUST
use these parameters when constructing the PIDF-LO document.
This element MAY be included in location requests, create context
requests and update context requests. When included in a location
request, the profile is used immediately; when used in create context
or update context requests, the profile is stored on the LS and is
provided to the LG when the LS responds to requests from LRs.
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Internet-Draft HELD March 20075.4.1. "presentity" Parameter
The "presentity" element contains a presentity identifier that the LG
SHOULD include in the "pres" attribute of the PIDF-LO document.
The LG MAY require authentication of the presentity through any
means; the LG SHOULD ignore this parameter if authentication
information is not present or authentication information cannot be
verified.
5.4.2. "retentionExpiry" Parameter
The "retentionExpiry" element contains an absolute "dateTime"
[W3C.REC-xmlschema-2-20041028] value for the "retention-expires"
element of the PIDF-LO usage rules. This element is mutually
exclusive with the "retentionInterval" element.
The LG MAY use a different value than that specified (or the
suggested default) as circumstances dictate, but MUST NOT use a value
later than specified. If this value indicates a time that has
already passed, the request MUST be rejected with an error. See
retentionInterval (Section 5.4.3) for more details.
5.4.3. "retentionInterval" Parameter
The "retentionInterval" element contains a time duration value that
is specified in the same fashion as the responseTime attribute
(Section 5.1).
This value MUST be added to the time at which the PIDF-LO document is
created to set the value of the "retention-expires" element. This
element enables the Target to set an interval over which a LR can
retain a LO, rather than an absolute time. This element is mutually
exclusive with the "retentionExpires" element.
If neither "retentionExpiry" nor "retentionInterval" are specified,
the LG SHOULD provide a default value for the "retention-expires"
element of the generated PIDF-LO document. The default for this
value SHOULD be 24 hours from the receipt of the location request as
defined in [RFC4119].
The LG MAY use a different value than that specified (or the
suggested default) as circumstances dictate, but MUST NOT use a value
larger than specified.
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Internet-Draft HELD March 20075.4.4. "retransmission" Parameter
The "retransmission" element contains a boolean value that MUST be
included in the "retransmission-allowed" element of the generated
PIDF-LO usage rules. When this element is not provided, the LG MUST
set the "retransmission-allowed" element to "false".
5.4.5. "rulesetURI" Parameter
The "rulesetURI" element contains a URI value that MUST be included
in the "ruleset-reference" element of the generated PIDF-LO usage
rules.
This datum is only used to construct the usage rules in the PIDF-LO
document. Within the context of a profile, this ruleset is not
applied by either LG or LS, and the LS does not apply the rules found
at the URI.
5.5. "signed" Parameter
The "signed" attribute indicates whether the Device requires a
digitally signed PIDF-LO. When present and set to "true", the LG
MUST provide a PIDF-LO document that is signed according to
[I-D.thomson-geopriv-location-dependability].
5.6. "lifetime" Parameter
The "lifetime" element specifies the maximum time that a context
should be maintained by the LS. This parameter MUST be included in
the context creation request to indicate to the LS the latest time
that the context is allowed to be retained. The parameter MAY be
included in context update requests to modify this time; when
included in an update request with a zero value, it indicates that
the context MUST be removed immediately.
The "lifetime" element is a duration value that is specified in the
same fashion as the "responseTime" attribute.
This value MUST be added to the current time when received by the LS
to determine the time at which the context expires. An LS MAY use
any value less than or equal to this value, but MUST NOT use a longer
value. The actual expiry time of the context MUST be indicated in
the context response.
5.7. "rules" Parameter
The "rules" element contains the authorization policy of the Target
that dictates how and to whom LI is provided by the LS. This policy
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MUST be applied by the LS when providing LI to LRs.
Authorization policies MUST conform to
[I-D.ietf-geopriv-common-policy]. If the authorization policy is
invalid, cannot be retrieved, or is otherwise not understood by the
LS, the LG SHOULD fail the request. Note that this implies that the
LS SHOULD attempt to retrieve an authorization policy that is
provided by-reference at the time of a create context request;
however, an LS MAY choose to do this later, if the requested response
time might be exceeded.
In the absence of an authorization policy, the LS MUST NOT provide LI
to any LR. Note that in certain jurisdictions an LS might be
required to provide LI to specific parties irrespective of the
authorization policy, as mandated by legislation; for example,
emergency services in some countries.
5.7.1. "rulesetURI" Parameter
The "rulesetURI" element contains a URI that references the Target's
authorization policy. This URI should reference a document of type
"application/auth-policy+xml" as defined in
[I-D.ietf-geopriv-common-policy].
It is RECOMMENDED that a ruleset URI use the "https" scheme. It is
anticipated that, to improve responsiveness and reduce network usage,
an LS could cache an authorization policy, consistent with the rules
specified by the Rule Holder. For instance, the Rule Holder could
specified retention times using the "Expires" header in HTTP
[RFC2616]. The impact of changes to authorization policies are
discussed in Section 4.3.2.
5.7.2. Common Policy "ruleset" Parameter
The "ruleset" element, which is in the
"urn:ietf:params:xml:ns:common-policy" namespace
[I-D.ietf-geopriv-common-policy], allows for providing an
authorization policy directly as part of a request.
5.8. "code" Parameter
All responses, except a PIDF-LO document, MUST contain a response
code. The "code" attribute applies to the "error" and
"contextResponse" messages.
The following response codes follow a three decimal form similar to
that in HTTP [RFC2616] and SIP [RFC3261]:
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200 (Success): This code indicates that the request was successful.
This code MUST not be used for an error response.
201 (Context Terminated): This code indicates that the request to
terminate a context was successful.
400 (Request Error): This code indicates that the request was badly
formed in some fashion.
401 (XML Error): This code indicates that the XML content of the
request was either badly formed or invalid.
402 (Authentication Error): This code indicates that the request
either did not contain authentication information, or the
authentication provided was not accepted.
403 (Asserted Location Error): This code indicates that the LI that
was asserted in the request was not acceptable to the LG. This
code is used when the "exact" attribute on the "assert" parameter
is set to "true".
404 (Context Not Found): This code indicates that the context
identified in the request was not found. This code MAY also be
used if the password provided was incorrect.
500 (General LG Error): This code indicates that an unspecified
error occurred at the LG.
501 (Location Unknown): This code indicates that the LG could not
determine the location of the Device.
502 (Unsupported Message): This code indicates that the request was
not supported or understood by the LG.
503 (Timeout): This code indicates that the LG could not satisfy the
request within the time specified in the "requestTime" parameter.
504 (Cannot Provide LI Type): This code indicates that the LG was
unable to provide LI of the type or types requested. This code is
used when the "exact" attribute on the "locationType" parameter is
set to "true".
Additional response codes within the x00 to x79 range MUST be
specified in published RFCs; the range from x80 to x99 is reserved
for private usage.
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Internet-Draft HELD March 20075.9. "message" Parameter
The "contextResponse" and "error" messages MAY include a "message"
attribute to convey some additional, human-readable information about
the result of the request. This message MAY be included in any
language, which SHOULD be indicated by the "xml:lang", attribute.
5.10. "context" Parameter
The "context" element includes information that is used to identify a
context and control access to it. The context is identified by one
or more Location URIs and a Device is granted a password which MUST
be provided when accessing the context to update the information
contained.
When a context is created, the LG provides a "contextResponse"
message that contains the "context" element. This element contains
all of the Location URIs that can be used for the context, a
password, and an expiry time.
To update the details in a context, or reuse profile information
stored in the context, the Device provides a "context" element. When
identifying a context in this manner, the Device MUST provide only
one Location URI and the password.
5.10.1. "locationURI" Parameter
The "locationURI" element includes a single Location URI. Each
Location URI is allocated by the LS so that it is able to uniquely
identify the context.
A "contextResponse" message contains any number of "locationURI"
elements. It is RECOMMENDED that the LS allocate a Location URI for
all schemes that it supports and that no scheme is present twice.
All "updateContext" request messages MUST contain only one
"locationURI" element, which is all that is necessary to uniquely
identify a context. The Device MAY select any of the Location URIs
provided by the LS. Location URIs do not change over the lifetime of
a context.
5.10.2. "password" Parameter
The "password" element carries a password that is used to access the
context after it has been created. The LS generates this value when
creating a context and the Device MUST use the exact same value when
it wishes to access the context. This value acts as a shared secret
between Device and LS.
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The value of the password MAY be updated in the response to any
"updateContext" message.
This element MAY contain any valid XML character data, within the
constraints of the XML Schema "token" type.
5.10.3. "expires" Parameter
The "expires" attribute indicates the time at which the context
created by the LS will expire. This attribute is included in the
"contextResponse" message only.
Responses to create and update context requests MUST include the
expiry time of the context. If the LS has expired a context in
response to an update context request, this value SHOULD include a
time in the past to avoid problems that could be caused by a slow
clock in the Device.
5.11. "location" Parameter
The "location" parameter is a boolean attribute associated with the
"createContext" or "updateContext" message. The default for this
attribute is "false".
This parameter, when present and set to "true" indicates that the LG
SHOULD include a PIDF-LO document in the "contextResponse" message.
The success of any request that includes this parameter MUST NOT be
affected by any error in providing a location; thus, if the LG is
unable to include a PIDF-LO, it is only omitted from the response.
If a "contextResponse" does not include a PIDF-LO, the Device can
determine the reasons for failure by sending a separate
"locationRequest".
Note: The schema does not include an explicit particle for the
"presence" element. This is because the "any" construct used to
allow for extensions would conflict with any optional element, due to
the Unique Particle Attribution schema rule.
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Internet-Draft HELD March 20077. HTTP Binding
This section defines an HTTP [RFC2616] binding for this protocol,
which all conforming implementations MUST support. This binding
takes the form of a Web Service (WS) that can be described by the Web
Services Description Language (WSDL) document in Section 7.1.
The three request messages are carried in this binding as the body of
an HTTP POST request. The MIME type of both request and response
bodies should be "application/held+xml", except that a PIDF-LO
document SHOULD have the MIME type "application/pidf+xml".
The LG populates the HTTP headers so that they are consistent with
the contents of the message. In particular, the "Expires" and cache
control headers are used to control the caching of any PIDF-LO
document. The HTTP status code SHOULD have the same first digit as
any "contextResponse" or "error" body included, and it SHOULD
indicate a 2xx series response when a PIDF-LO document is included.
This binding also includes a default behaviour, which is triggered by
a GET request, or a POST with no request body. If either of these
queries are received, the LG MUST attempt to provide a PIDF-LO
document, as if the request was a location request.
This binding MUST use TLS as described in [RFC2818]. TLS provides
message integrity and privacy between Device and LG. The LG MUST use
the server authentication method described in [RFC2818]; the Device
MUST fail a request if server authentication fails, except in the
event of an emergency.
7.1. HTTP Binding WSDL
The following WSDL 2.0 [W3C.CR-wsdl20-20060106] document describes
the HTTP binding for this protocol. Actual service instances MUST
provide a "service" with at least one "endpoint" that implements the
"heldHTTP" binding. A service description document MAY include this
schema directly or by using the "import" or "include" directives.
<?xml version="1.0"?>
<wsdl:definitions
xmlns:wsdl="http://www.w3.org/2005/05/wsdl"
xmlns:whttp="http://www.w3.org/2005/05/wsdl/http"
xmlns:held="urn:ietf:params:xml:ns:geopriv:held"
xmlns:pidf="urn:ietf:params:xml:ns:pidf"
xmlns:heldhttp="urn:ietf:params:xml:ns:geopriv:held:http"
targetNamespace="urn:ietf:params:xml:ns:geopriv:held:http"
type="http://www.w3.org/2005/05/wsdl/http">
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Internet-Draft HELD March 20078. Security Considerations
The threat model for this protocol assumes that the LG exists within
the same administrative domain as the Device. The LG requires access
to network information so that it can determine LI. Therefore, the
LG can use network information to protect against a number of the
possible attacks.
Specific requirements and security considerations ofr location
acquisition protocols provided in [I-D.ietf-geopriv-l7-lcp-ps].
An in-depth discussion of the security considerations applicable to
the use of Location URIs and by-reference provision of LI is included
in [I-D.marshall-geopriv-lbyr-requirements].
8.1. Return Routability
It is RECOMMENDED that Location Generators use return routability
rather than requiring Device authentication. Device authentication
SHOULD NOT be required due to the administrative challenge of issuing
and managing of client credentials, particularly when networks allow
visiting users to attach devices. However, the LG MAY require any
form of authentication as long as these factors are considered.
Addressing information used in a request to the LG is used to
determine the identity of the Device, and to address a response.
This ensures that a Device can only request its own LI.
A temporary spoofing of IP address could mean that a device could
request a Location URI that would result in another Device's
location. One or more of the follow approaches are RECOMMENDED to
limit this exposure:
o Location URIs SHOULD have a limited lifetime, that is, the LG
SHOULD enforce a maximum value for the lifetime element
(Section 5.6).
o The network SHOULD have mechanisms that protect against IP address
spoofing.
o The LG SHOULD ensure that requests can only originate from within
its administrative domain.
o The LG and network SHOULD be configured so that the LG is made
aware of Device movement within the network and addressing
changes. If the LG and LS detect a change in the network that
invalidates a context, the context MUST be terminated.
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The above measures are dependent on network configuration and SHOULD
be considered with circumstances in mind. For instance, in a fixed
internet access providers may be able to restriction the allocation
of IP addresses to a single physical line, ensuring that spoofing is
not possible; in such an environment, the other measures are not
necessary.
8.2. Transaction Layer Security
All bindings for this protocol MUST ensure that messages are
adequately protected against eavesdropping and modification.
Bindings MUST also provide a means of authenticating the LG.
It is RECOMMENDED that all bindings also use TLS [RFC2246].
For the HTTP binding, TLS MUST be used. TLS provides protection
against eavesdropping and modification. The server authentication
methods described in HTTP on TLS [RFC2818] MUST be used.
8.3. Veracity of Asserted LI
The assert element (Section 5.2) allows a Device the ability to
provide LI. However, if an LG uses asserted LI, it is the LG that
becomes responsible for the veracity of that information. Therefore,
when the Device provides LI in a request, the LG MUST NOT use this
information unless it can ensure its accuracy. This prevents the
fraudulent provision of LI that could be caused by the LG accepting
LI without any checks.
It is unlikely that an LG is able to verify Device-provided LI beyond
any uncertainty. The ability of an LG to verify LI is limited by its
own capacity to determine the location of the Device. The LG SHOULD
indicate the source of LI using the PIDF-LO "method" parameter so
that users of LI can make appropriate judgments on its veracity.
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Internet-Draft HELD March 20079. Examples9.1. Simple HTTP Binding Example Messages
The examples in this section show a complete HTTP message that
includes the HELD request or response document.
This example shows the most basic request for a LO. This uses the
GET feature described by the HTTP binding. This example assumes that
the LG service exists at the URL "https://lg.example.com/location".
GET /location HTTP/1.1
Host: lg.example.com
Accept: application/pidf+xml,application/held+xml,application/xml;q=0.8,
text/xml;q=0.7
Accept-Charset: UTF-8,*
The GET request is exactly identical to a minimal POST request that
includes an empty "locationRequest" element.
POST /location HTTP/1.1
Host: lg.example.com
Accept: application/pidf+xml,application/held+xml,application/xml;q=0.8,
text/xml;q=0.7
Accept-Charset: UTF-8,*
Content-Type: application/held+xml
Content-Length: 87
<?xml version="1.0"?>
<locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"/>
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Note: To focus on important portions of messages, all examples
following this note do not show HTTP headers or the XML prologue.
In addition, sections of XML not relevant to the example are
replaced with comments.
9.2. Location Request Examples
The location request shown below specifies location types and
provides a profile that the LG applies to the PIDF-LO document. The
request specifies that a response is desired within 10.5 seconds.
<locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"
responseTime="PT10.5S" signed="false">
<locationType exact="true">
jurisdictionalCivic
geodetic
</locationType>
<profile>
<presentity>pres:user@example.com</presentity>
<retentionInterval>1800</retentionInterval>
<retransmission>false</retransmission>
<rulesetURI>https://example.com/~user/ruleset.xml</rulesetURI>
</profile>
</locationRequest>
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The following location request includes a location assertion that
includes a user-provided civic address. This message also requests
that the LG retrieve profile information from a context that exists
on an LS.
<locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"
responseTime="2">
<assert method="Manual" exact="true">
<civicAddress
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xml:lang="en-AU">
<!-- civic address contents -->
</civicAddress>
</assert>
<context>
<locationURI>
https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
</locationURI>
<password>vs76e8cae9873a079888p9y4txwa</password>
</context>
</locationRequest>
Since this request includes the "exact" parameter set to "true", any
successful response MUST include the provided LI.
9.3. Context Creation and Update Examples
The following create context request shows the simplest form of this
message, which sets a two hour lifetime on the context and includes a
"rulesetURI" element for the LS.
<createContext xmlns="urn:ietf:params:xml:ns:geopriv:held">
<lifetime>PT2H</lifetime>
<rules>
<rulesetURI>
https://www.example.com/~user/privacy/ruleset.xml
</rulesetURI>
</rules>
</createContext>
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The following more complex create context request includes additional
information. This includes a profile that sets the presentity and
some of the "usage-rules" components in the PIDF-LO that the LS
serves.
<createContext xmlns="urn:ietf:params:xml:ns:geopriv:held">
<lifetime>PT2H</lifetime>
<profile>
<presentity>pres:user@example.com</presentity>
<retentionExpiry>2006-01-13T12:00:00+00:00</retentionExpiry>
<retransmission>false</retransmission>
</profile>
<rules>
<rulesetURI>
https://www.example.com/~user/privacy/ruleset.xml
</rulesetURI>
</rules>
</createContext>
A typical successful response to this message provides several
Location URIs in different schemes (in this case: "https" and
"sips"), the exact context expiry time, and a password that can be
used to update the context.
<contextResponse xmlns="urn:ietf:params:xml:ns:geopriv:held"
code="200" message="OK">
<context expires="2006-01-11T05:38:01+00:00">
<locationURI>
https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
</locationURI>
<locationURI>
sips://ls.example.com:9769/357yc6s64ceyoiuy5ax3o
</locationURI>
<password>38cdj38mjcd-0-=54821kj28mp1qms.1</password>
</context>
</contextResponse>
If any aspect of the data stored in a context changes, a
"contextUpdate" request is sent to the LG to request that it update
the information. This request includes the information necessary to
access a context (the location URI and password) and only the
information that has changed.
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The following request demonstrates how information stored in a
context could be updated. For the context previously created, this
provides the "retentionInterval" element, which overrides a
previously configured "retentionExpiry" value.
<updateContext xmlns="urn:ietf:params:xml:ns:geopriv:held"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<context>
<locationURI>
https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
</locationURI>
<password>38cdj38mjcd-0-=54821kj28mp1qms.1</password>
</context>
<profile>
<retentionInterval>600</retentionInterval>
</profile>
</updateContext>
To indicate success, the LG provides a "contextResponse" identical in
form to the original request.
The following request shows that a context lifetime can be extended
or shortened by the Device by updating a context with a new
"lifetime" element. The following message requests that the LS
maintain the context for two hours beyond the current time.
<updateContext xmlns="urn:ietf:params:xml:ns:geopriv:held">
<context>
<locationURI>
https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
</locationURI>
<password>38cdj38mjcd-0-=54821kj28mp1qms.1</password>
</context>
<lifetime>PT2H</lifetime>
</updateContext>
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The response to a request to extend the context includes the new
expiry time of the context, if it has changed.
<contextResponse xmlns="urn:ietf:params:xml:ns:geopriv:held"
code="200" message="OK">
<context expires="2006-01-11T05:39:46+00:00">
<locationURI>
https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
</locationURI>
<locationURI>
sips://ls.example.com:9769/357yc6s64ceyoiuy5ax3o
</locationURI>
<password>38cdj38mjcd-0-=54821kj28mp1qms.1</password>
</context>
</contextResponse>
A zero value for the "lifetime" element terminates the context. The
following request terminates the context.
<updateContext xmlns="urn:ietf:params:xml:ns:geopriv:held">
<context>
<locationURI>
https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
</locationURI>
<password>38cdj38mjcd-0-=54821kj28mp1qms.1</password>
</context>
<lifetime>PT0S</lifetime>
</updateContext>
The response to a message that requests the termination of a context
appears as follows.
<contextResponse xmlns="urn:ietf:params:xml:ns:geopriv:held"
code="201" message="Context removed"/>
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Internet-Draft HELD March 20079.4. Sample LG WSDL Document
The following WSDL document demonstrates how a WSDL document can be
created for a specific service, in this case, a service at the URI
"https://lg.example.com/location".
<?xml version="1.0"?>
<wsdl:definitions
xmlns:wsdl="http://www.w3.org/2005/05/wsdl"
xmlns:heldhttp="urn:ietf:params:xml:ns:geopriv:held:http"
targetNamespace="http://lg.example.com/ws/held">
<wsdl:import
namespace="urn:ietf:params:xml:ns:geopriv:held:http"/>
<wsdl:service name="sample-held-svc" interface="heldhttp:held">
<wsdl:endpoint name="sample-held-ep"
binding="heldhttp:heldHTTP"
address="https://lg.example.com/location"/>
</wsdl:service>
</wsdl:definitions>
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Internet-Draft HELD March 200710. IANA Considerations
According to the guidelines in [RFC3688], this document calls for an
IANA registry for result codes and registers an XML namespace and
schema. It also registers the "application/held+xml" MIME type.
10.1. IANA Registry for HELD Result Codes
IANA will establish and maintain a registry of HELD result codes.
Additional values are registered based on the "specification
required" option in [RFC3688].
Specifications MUST specify the following information when
registering new values in this registry:
Code Value: A three-digit value from 000 to 679. The last 20 codes
in each block of 100 (from x80 to x99) are reserved for private or
experimental use and cannot be registered.
Short Message: A brief message that describes the general reason for
the code.
Publication: A reference to any relevant publication or
specification.
Description and Usage: A longer description of the code and the
circumstances where it applies. This description does not need to
be exhaustive.
The values in Section 5.8 are pre-registered in this registry.
10.2. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:geopriv:held
This section registers a new XML namespace,
"urn:ietf:params:xml:ns:geopriv:held", as per the guidelines in
[RFC3688].
URI: urn:ietf:params:xml:ns:geopriv:held
Registrant Contact: IETF, GEOPRIV working group,
(geopriv@ietf.org), Martin Thomson (martin.thomson@andrew.com).
XML:
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Interoperability considerations: This content type provides a basis
for a protocol
Published specification: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please
replace XXXX with the RFC number for this specification.]]
Applications which use this media type: Location information
providers and consumers.
Additional Information: Magic Number(s): (none)
File extension(s): .xml
Macintosh File Type Code(s): (none)
Person & email address to contact for further information: Martin
Thomson <martin.thomson@andrew.com>
Intended usage: LIMITED USE
Author/Change controller: This specification is TBD
Other information: This media type is a specialization of
application/xml [RFC3023], and many of the considerations
described there also apply to application/held+xml.
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Internet-Draft HELD March 2007Appendix A. HELD Compliance to IETF LCP requirements
This appendix describes HELD's compliance to the requirements
specified in the [I-D.ietf-geopriv-l7-lcp-ps]. In addition to the
LCP requirements specified by the IETF, HELD has independently been
assessed against and found to comply with all the NENA requirements
for a location acqusition protocol defined in [NENA_TID].
A.1. L7-1: Identifier Choice
"The LIS MUST be presented with a unique identifier of its own
addressing realm associated in some way with the physical location of
the end host."
COMPLY
The identifier used may be the source address of the request packet
and/or additional client identifier values relevant to the scope of
the access network provided within the request. Mapping an IP
address into lower-level attachment data is access network dependent
and is the responsibility the LIS. HELD can however be used to
provide assistence to the LIS through the inclusion of identity
extensions such as those defined in
[I-D.winterbottom-geopriv-held-identity-extensions].
A.2. L7-2: Mobility Support
"The GEOPRIV Layer 7 Location Configuration Protocol MUST support a
broad range of mobility from devices that can only move between
reboots, to devices that can change attachment points with the impact
that their IP address is changed, to devices that do not change their
IP address while roaming, to devices that continuously move by being
attached to the same network attachment point."
COMPLY
Mobility support is inherently a characteristic of the access network
technology and HELD is designed to be access network agnostic.
Consequently HELD complies with this requirement. In addition HELD
provides specific support for mobile environments by providing an
optional responseTime attribute in location request messages.
Wireless networks often have several different mechanisms at their
disposal for position determination (e.g. Assisted GPS versus
location based on serving base station identity), each providing
different degrees of accuracy and taking different amounts of time to
yield a result. The responseTime parameter provides the LIS with a
criterion which it can use to select a location determination
technique.
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HELD also supports an extension mechanism that allows location
measurement capabilities to be exchanged between the end-point and
the LIS. This mechanism allows for a greater number of location
determination techniques to be used by both the end-point and the
LIS. The specification describing this capability is provided in
[I-D.thomson-geopriv-held-capabilities].
A.3. L7-3: Layer 7 and Layer 2/3 Provider Relationship
"The design of the GEOPRIV Layer 7 Location Configuration Protocol
MUST NOT assume a business or trust relationship between the provider
of application layer (e.g., SIP, XMPP, H.323) provider and the access
network provider operating the LIS."
COMPLY
HELD describes a location acquisition protocol and has no
dependencies on how location is used once it has been acquired.
Location acquisition using HELD is subject to the restrictions
described in Section 8.
A.4. L7-4: Layer 2 and Layer 3 Provider Relationship
"The design of the GEOPRIV Layer 7 Location Configuration Protocol
MUST assume that there is a trust and business relationship between
the L2 and the L3 provider. The L3 provider operates the LIS and
needs to obtain location information from the L2 provider since this
one is closest to the end host. If the L2 and L3 provider for the
same host are different entities, they cooperate for the purposes
needed to determine end system locations."
COMPLY
HELD was specifically designed with this model in mind and readily
allows itself to chaining requests between operators without a change
in protocol being required. Examples of how HELD can be used in this
manner are provided in detail in [NENA_TID]. HELD is a webservices
protocol it can be bound to transports other than HTTP, for example a
BEEP binding for HELD, [I-D.thomson-geopriv-held-beep]. Using a
transport like BEEP for HELD offers the option of high request
throughput over a dedicated connection between an L3 provider and an
L2 provider without incurring the serial restriction imposed by HTTP.
This is less easy to do with protocols that do not decouple
themselves from the transport.
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Internet-Draft HELD March 2007A.5. L7-5: Legacy Device Considerations
"The design of the GEOPRIV Layer 7 Location Configuration Protocol
MUST consider legacy residential NAT devices and NTEs in an DSL
environment that cannot be upgraded to support additional protocols,
for example to pass additional information through DHCP."
COMPLY
HELD is an application protocol and operates on top of IP. A HELD
request from a host behind a residential NAT will traverse the NAT
acquiring the external address of the home router. The location
provided to the host therefore will be the address of the home router
in this circumstance. No changes are required to the home router in
order to support this function, HELD was designed specifically to
address this deployment scenario. Examples of how HELD can be used
in this type of network environment are provided in [NENA_TID].
A.6. L7-6: VPN Awareness
"The design of the GEOPRIV Layer 7 Location Configuration Protocol
MUST assume that at least one end of a VPN is aware of the VPN
functionality. In an enterprise scenario, the enterprise side will
provide the LIS used by the client and can thereby detect whether the
LIS request was initiated through a VPN tunnel."
COMPLY
HELD does not preclude a LIS on the far end of a VPN tunnel being
aware that the client request is occurring over that tunnel. It also
does not preclude a client device from accessing a LIS serving the
local physical network and subsequently using the location
information with an application that is accessed over a VPN tunnel.
A.7. L7-7: Network Access Authentication
"The design of the GEOPRIV Layer 7 Location Configuration Protocol
MUST NOT assume prior network access authentication."
COMPLY
HELD makes no assumptions about prior network access authentication.
HELD strongly recommends the use of TLS with server-side certificates
for communication between the end-point and the LIS. There is no
requirement for the end-point to authenticate with the LIS.
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Internet-Draft HELD March 2007A.8. L7-8: Network Topology Unawareness
"The design of the GEOPRIV Layer 7 Location Configuration Protocol
MUST NOT assume end systems being aware of the access network
topology. End systems are, however, able to determine their public
IP address(es) via mechanisms such as STUN or NSIS NATFW NSLP."
COMPLY
HELD makes no assumption about the network topology. HELD doesn't
require that the device know its external IP address, except where
that is required for discovery of the LIS. LIS disocvery techniques
available to a HELD client are described in
[I-D.thomson-geopriv-lis-discovery]. In certain network environments
an end-point maybe able to ascertain information about the topology
of the access network which may assist the LIS in location
determination. HELD provides support for extensions that allow this
information to be communicated to the LIS when it is available.
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Internet-Draft HELD March 2007Appendix B. HELD Compliance to NENA Location Acqusition Requirements
This section details how HELD complies to each of the requirements
provided in section 4 of [NENA_TID].
B.1. DA1
"The access network shall provide a mechanism for determination and
acquisition of location information, and support queries for
location."
COMPLY
HELD provides location acqusition functionality. A LIS may use any
means to obtain measurements from the network to assist with location
determination.
B.2. DA2
"The location estimate used shall be that associated with the
physically (wire, fiber, air) connected network."
COMPLY
HELD is designed to support the acquisition of location information
determined on the basis of the physical access network with which the
device is associated. HELD does not preclude any specific technology
used by that access.
B.3. DA3
"Location may be requested at any time. Location information must be
associated with the device at the time the location is requested."
COMPLY
HELD location requests can be made at any time to the identified LIS
serving the access network. It is the responsibility of the LIS to
use the IP address and/or other identifiers included in the location
request and determine the current location of the Target. Where more
than one determination technology is available, the requesting entity
may specify a response time to assist the LIS in selecting the
appropriate location determination technology to use. The HELD
protocol does not impose any physical constraints that prevent the
LIS from reassessing the location at the time of each request.
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Internet-Draft HELD March 2007B.4. DA4
"Location acquisition should be provided by a consistent method
across all network configurations."
COMPLY
HELD requires an end-point to be able to discover the LIS in the
local access network. Once the LIS is known HELD is access network
agnostic and can be used in the same way in any network topology.
B.5. DA5
"Location determination and acquisition mechanisms must be applicable
to emergency calling, and may also be applicable to a wide range of
value-added location-based services."
COMPLY
HELD has specific semantics defined for obtaining locations suitable
for routing emergency calls. In particular, HELD provides a rich set
of location request options so that an application can retrieve
location information in the form most suitable for its purpose.
B.6. DA6
"Location determination and acquisition techniques shall support both
NENA i2 and i3 network architectures."
COMPLY
HELD provides all of the functions necessary to support emergency
calling applications. HELD has a specific semantic for requesting
location information suitable to inclusion in emergency calling
applications. Location information acquired using HELD is contained
in a PIDF-LO the form required by both the NENA i2 and i3
architectures. It also supports location by reference mechanisms for
out-of-band mid-call location updates as required, for example, for
mobile wireless networks.
B.7. DA7
"When measurement based-location determination mechanisms fail, the
most accurate location information available should be provided.
Examples include: For mobile, the Wireless Service Provider might
provide tower or Access Point location, last known fix, etc. For
wireline, a LIS might provide a civic location that defines the
serving area of an access point, e.g., the State of Texas."
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Not Applicable
HELD is a location acqusition protocol and will return the location
determined by the LIS. HELD does not preclude the LIS from applying
any arbitrarily sophisticated set of location determination
techniques and associated fallback policy appropriate to the access
technology it supports.
B.8. DA8
"Location determination and acquisition must provide minimal impact
to call setup time in the event that location is not known ahead of
time."
COMPLY
HELD allows a location to be requested at any time, including prior
to or during a call. Where time is of the essence the requesting
entity can provide a response time indicating to the LIS that
location is needed in the period specified. This allows the LIS to
select the most accurate location determination technology available
to it that can yield a location in the allotted time. This is of
particular importance in wireless networks where the most accurate
location determination techniques may take 10s of seconds.
B.9. DA9
"Where a device is not location aware the IP Access network should
have the ability to provide a location estimate on behalf of the
device."
COMPLY
In order to support this functionality the requesting node must have
a pre-existing trust relationship with the LIS, and HELD identity
extensions as described in
[I-D.winterbottom-geopriv-held-identity-extensions]. Where these
requirements are satisfied, the LIS may provide a HELD response to
the requesting device that has the same form as if the target device
had been the requestor. If the traffic volume between the trusted
node and the LIS is likely to be high, the HELD BEEP binding
[I-D.thomson-geopriv-held-beep] may be used.
B.10. DA10
"Location acquisition methods should not require modification of
hardware/firmware in home-routers or modems."
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COMPLY
This requirement is essentially the same as Appendix A.5. HELD is an
application protocol and operates on top of IP. A HELD request from
a host behind a residential NAT will traverse the NAT acquiring the
external address of the home router. The location provided to the
host therefore will be the address of the home router in this
circumstance. No changes are required to the home router in order to
support this function, HELD was designed specifically to address this
deployment scenario.
B.11. DA11
"A location determination method must exist that does not require
network hardware replacement."
Not Applicable
HELD is a location acquisition protocol and does not directly specify
how location is determined in the network. However, HELD does not
require additions to or replacement of existing network server
implementations because it is not defined as an extension to any
existing non-location service protocol.
B.12. DA12
"The location acquisition protocol shall allow the requesting device
to specify a response time requirement to the LIS when requesting
location information. The response time is expressed as the maximum
time that the requesting node is prepared to wait for location
information. The LIS is required to provide the most accurate
location fix it can within the specified response time."
COMPLY
HELD has an explicit "responseTime" parameter that can be used with
any request to the LIS. This parameter provides an indication to the
LIS of how long the requesting node is prepared to wait for location,
allowing the LIS to select the appropriate location determination
technology to invoke particularly where it may need to trade off the
accuracy of the result to meet the time constraint.
B.13. Rep1
"Location information may be provided as location-by-value or
location-by-reference and the form is subject to the nature of the
request."
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COMPLY
HELD supports requesting either a location reference in the form a
location URI and/or a literal location. Literal locations are
provided as a PIDF-LO.
B.14. Rep2
"Location determination and acquisition mechanisms must support all
location information fields defined within a PIDF-LO."
COMPLY
HELD provides location information in the form of a PIDF-LO,
consequently all PIDF-LO fields are implicitly supported.
B.15. Rep3
"Location acquisition mechanisms must allow for easy backwards
compatibility as the representation of location information evolves."
COMPLY
HELD provides location as a PIDF-LO, any changes made to the PIDF-LO
definition are made independently and without impact to the HELD
definition.
B.16. Rep4
"All representations of location shall include the ability to carry
altitude and/or floor designation. This requirement does not imply
altitude and/or floor designation is always used or supplied."
COMPLY
The PIDF-LO has explicit support for both civic and geodtic location
types and consequently provides support for encoding both altitude
and building floor values. Since HELD provides location as a
PIDF-LO, any location that can be expressed in a PIDF-LO is
compatible with HELD. HELD recommends that PIDF-LOs be constructed
in accordance with the rules laid out in
[I-D.ietf-geopriv-pdif-lo-profile].
B.17. LocSec1
"Location information shall only be provided to authenticated and
authorized network devices. The degree of authentication and
authorization required may vary depending on the network."
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COMPLY
A LIS generally authenticates a Target using HELD to request its own
location implicitly. Authentication is based on the IP address of
the source request packet, inband indentifiers, and return
routability. Where this level of authentication is not deemed
sufficient other authentications mechanisms can be used, such as
client-side certificates, shared-secret keys and HTTP digest.
B.18. LocSec2
"Location determination and acquisition methods should preserve
privacy of location information, subject to local laws and
regulations."
COMPLY
This requirement is of particular significance where the acqusition
protocol is also being used as a dereference protocol for a location
URI. HELD supports this function by allowing a Target to provide
access rules to the LIS. The Target may provide either an explicit
set of rules defined using common policy syntax as described in
[I-D.ietf-geopriv-common-policy], or the Target may provide a ruleset
URI allowing the LIS to retrieve the ruleset from a third-party. LIS
operators are also able to provide a default set of overiding
policies to support, for example, emergency services. How these
additional rules are provisioned and applied is a matter of LIS
implementation and is outside the scope of any location acquisition
protocol.
B.19. LocSec3
"The location or location estimate of a caller should be dependable."
COMPLY
HELD supports this through two mechanisms. The first is a "signed"
attribute that can be included with a location request. This allows
the user to explicitly request a signed location object. The second
is through location assertion. This allows an end-point to proffer a
location to the LIS, and for the LIS to assert this location against
the location that the LIS would provide. The assert function is
described in more detail in Section 5.2.
B.20. LocSec4
"The location acquisition protocol must support authentication of the
Location Information Server, integrity protection of the Location
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Information, and protection against replay."
COMPLY
HELD recommends the use of TLS with server-side certificates for LIS
authentication to requesting nodes where considered necessary. TLS
when used in this fashion mitigates the risks of impersonation of the
LIS. TLS also provides confidentiality and replay protection for
requests and location information.
B.21. LocSec5
"The location source shall be identified and should be authenticated.
This includes manually entered location."
COMPLY
HELD provides a "signed" attribute that can be used to request a
signed location object as described in Section 5.5. For Target
provided locations, be for manually entered or device-determined
location, HELD provides the location assertion function, which when
combined with the "signed" attribute provides location source
identification and authentication.
B.22. LocSec6
"Where a location is acquired and cached prior to an emergency call,
it should be refreshed at regular intervals to ensure that it is as
current as possible, in the event location information cannot be
obtained in real time."
COMPLY
HELD supports the ability to request location at any time.
B.23. LocSec7
"Where location by-reference is used the appropriate privacy policies
must be implemented and enforced by the LIS operator."
COMPLY
HELD allows a Target to provide access rules ot the LIS. The Target
may provide either an explicit set of rules defined using common
policy syntax as described in [I-D.ietf-geopriv-common-policy], or
the Target may provide a ruleset URI allowing the LIS to retrieve the
ruleset from a third-party.
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